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Pented July 15, 12H9 UNITED STATES lPATENT OFFICE.

FREDERICK W. SPERR, JR., OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO H.'KOP- PERs COMPANY, VANIA.

OllE ITTSBURGH, PENNSYLVANIA, vA, CORPORATION OF PENN SYL- MANUFACTURE0F AMMONIUM .SULFA'I' Specification of Letters Patent.

Patented July 15, 1919.

Application mea May 1o. 191s. seriai No. 233,675.

.produce ammonium sulfate whichis practically free of free acid.

Ammoniumv sulfate, as commonly prepared by absorbing ammonium vapors insulfuric acid and subsequent separation of the ammoniuni sulfatecrystals from the acid liquor, contains a certain proportion of freesulfuric acid. lThe usual practice is to .sepa-' 'rate the ammoniumsulfate crystals from the parent liquor by means of a centrifugal drier;and in order to free the .crystals from as much acid as possible, theyare Washed in the drier with a small quantity ofwater.

By careful treatment, it, is possible to obtain ammonium sulfate in thismanner having as low as .15% free acid, but it has not been found'practicable by ordinary methods to obtain a material having less thanthis percentage of acid, and the usual practice produces commercialammonium sulfate containing from .2 to .4% free acid.

Among the various means that have been proposed for producing a neutralammonium sulfate free from uncombined sulfuric acid, the mostpracticable of which I am aware consists in washing the ammonium sulfatecrystals immediately afterthey have been separated from the motherliquor in the centrifuge or other separating apparatus with a crude,weak ammonia liquor, such as the gas liquor which is usually availablein large quantities. This practice.however, has several objections, asthe crude liquor always contains sulfur compounds which react with smallquantities of iron sulfatey which thx ammonium sulfate usually contains,thereby forming iron suld which discolors the crystals. Crude ammonialiquor also usually contains cyanid compounds, and these producecompounds with iron which are colored a deep blue. Furthermore, the

'crude liquor also frequently contains tar oils, phenols and otherimpurities which have a bad effect o'n monium sulfate. i

I haveV found it possible to overcome these objectlons and to -produ'cea neutral ammonium sulfate, by washing or treating the ammonium sulfatecrystals, after their separation from the mother liquor by an ammoma'liquor or vapor which has been largely freed of its 1mpurities andwhich may be produced from that part of the ordinary ammonia still whichis known asthe fixed still. i

In the. accompanying diagram, I have shown such a still, together with ageneral i arrangement of other apparatus necessary to the practice of myinvention. The o eration of such a. still and the apparatus is.generally as follows:

Steam is admitted to the lower section of the fixed still 2, through thepipe l, and p asses upwardly through thel various sections of this stilland then through the pipe 3 and the lower section of the. free still 4,au'd thence upwardly through the sections of this tree. still to theexit pipe The crude, weak liquor is admitted to the upper seetion of thefree still Ithrough pipe 6 and flows downwardly through the sections of.

this still into the tank 7, which forms the base ofthe still. This tankis usually designated as the lime leg. In this tank the liquor is mixedwitlrasuitable quantity 0f milk ot' lime whicll is fed in through thepipe 8. The mixture passes through the pipe 9 to the top section of thefixed Still, and finally flows out through the exit 10.v

The operation of the still such that all of the volatile ammoniacompounds, together with the volatile impurities, are removed by theaction of the steam and vapors passing; upwardly through the free still.The ixcd compounds of the ammonia, such as ammonium chlorid, ammoniumsulfate', etc., arel decomposed by the action of the lime the quality ofthe amin the lime leg. The .vapors from the fixed used for theneutralization of the free acid in the ammonium sulfate, without dangerof contaminating the product.

In accordance with my invention, a part of `the vapors from the fixedstill 2 are caused to pass into the water-cooled reflux condenser 11. Inthis condenser, the vapors are concentrated, giving a higher percentageof ammonia, and some of the steam `condenses and goes back into thefixed still. By varying the amount. of water used in the condenser, thestrength of the ammonia liquor produced may be regulated withinsatisfactory limits. The vapors pass through the reflux condenser, andthence through the water-cooled condenser 12 into the mixing chamber 13having the water supply connection l-I. The final strength of the liquoris regulated by theamount of water 4added to this tank. The mixing tankmayl be provided with any suitable mechanical or air-stirring apparatus.From the mixing tank, the liquor flows through the feed pipe 15, to theblowing tank 16, which is equipped with steam coils for heating theliquor to the proper temperature. The blowing tank is operated bycompressed air which is admitted through the pipe 17, and by means of'wliielitlie purified ammonia liquor is discharged through a suitableconnection on to the crystals jin the centrifugal drier 18.

It will be understood that the apparatus which I have 'diagrammaticallyshown is illustrative only,"and that any suitable apparatus may beemployed to utilize the vapors from the fixed still to neutralize freeacid in theannnonium sulfate.

I have found it preferable to prepare, for

vthe purpose of this invention, a weak ammonia solution containing fromone to three grams of ammonia'per liter,l and to use such solution at atemperature of from 80 to 90 G. inthe blowing tank. The temperature may,however, be raised to a higher degree, and in-"fact, the solution may beused either hot or cold.LV I have found -that the application of'such asolution in -the form of a good spray to a five hundred pound 4batchgofammonium sulfate in the centrifuge for from fifteen to twenty secondsgives a good, white, neutral product corr taining practically no freeacid or ammonia.

I have found such washes to require as lit-A .tle'as two gallons of'ammonia solution for five hundred pounds of ammonium sulfate.

The weak ainn'ionia solution is very stable even when kept heated at 90oC. The various tanks should be made vapor-tight in order to prevent lossof ammonia vapors.

My process is a very easy one to employ .because practically everyammonium sulfate plant is equipped with an ammonia still. rI`lie mainproduct ot' the an'nnonia still may be utilized for other purposes, onlya small amount of the vapors from the fixed still being necessary tocarry out my process. 5

Instead of using the ammonia in the forni otl a weak liquor, goodresults may be ob` tained by treating the annnoniuni sulfate crystalswith ammonia in the forni of a vapor. This vapor 'an be taken off just.beyond the reflux condenser, and the crystals may be treated with it inany desired manner.

In the appended claims, wherein I refer to the treatment of ammoniumsulfate with ammonia, it is to 'be understood that the.

fate, the method of' preparing a neutralizing agent for treatingammonium sulfate crysi tals, which consists in taking vapors from thefixed section of an ammonia still, and

forming an ammonia'liquor therefrom for' the treatment of' suchcrystals, substantially as described.

3: In the manufacture of ammonium sulfate, the method of' preparing aneutralizing agent for treating ammonium sulfate crystals, whichconsists in taking vapors` from a fixed section of an ammonia still,conion densing and concentrating the saine, and

forming an ammonia liquor therefrom for the treatment of such crystals,substantially as described.

4. In the manufacture of ammonium sulfate, the method ot' preparing aneutralizing agent. for treating auinfionium sulfate crystals, whichconsists iii-taking vapors from a fixed section of aniammonia still,condens-y ing and concentrating the same,forniiiig `l an ammonia liquortherefrom, and regulat ing the strength and temperature of' such liquorfor the treatment ot' such crystals. substantially as described.

In testimony whereof, I have hereunto set my hand.

FREDERICK W. SPERR, JR.

